Compliance meter for respiratory therapy

ABSTRACT

A respiratory apparatus (10) operable for delivering a breathable gas to the airway of a patient includes a status monitor (24,26) for determining the status of usage of the unit by the patient and a timer (32) for determining the accumulated time of usage of the unit by the patient.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the field of respiratory therapy. Moreparticularly, the invention concerns a respiratory apparatus operablefor delivering a breathable gas to the airway of a patient and includesa status monitor for determining the status of usage of the unit by thepatient and a timer for determining the accumulated time of usage of theunit by the patient.

2. Description of the Prior Art

In the treatment of obstructive sleep apnea, for example, it has beenfound that the application of pressurized ambient air to the nasalpassages of a patient provides a pneumatic splint that maintains thepatency of the airway. This type of respiratory therapy can beimplemented by a home therapy device having a blower unit, a nasal mask,and a pneumatic hose interconnecting the two. When the patient is readyto retire for the night, the mask is placed in position over thepatient's nose and the blower activated to deliver the prescribedtherapeutic pressure regimen to the patient's airway. The prescribedtherapy may include continuous positive air pressure (CPAP),intermittent positive air pressure (IPAP), or a variety of otherpressure regimens, depending upon the needs of the patient.

As those skilled in the art appreciate, the effectiveness of an apneatherapy device depends upon its usage. In order to determine usage, someprior art devices have incorporated a timer which indicates accumulatedoperational time of the device. Such prior art devices, however, do notdetermine whether the device has actually been used by the patient. Eventhough the therapy device has been turned on, the patient may not haveused the device or the nasal mask may have become dislodged during thesleep session.

SUMMARY OF THE INVENTION

The present invention solves the prior art problems discussed above andprovides a distinct advance in the state of the art. More particularly,the present invention determines the accumulated time of actual usage ofa respiratory apparatus.

The preferred respiratory apparatus includes a gas delivery unitoperable for coupling with the airway of a patient in delivering abreathable gas thereto, a status monitor for monitoring a parameterindicative of the status of usage of the delivery unit, and a timerresponsive to the status monitor for determining the accumulated time ofusage of the delivery unit by the patient. In one embodiment of theinvention, the status monitor includes a pressure sensor for sensing thepressure at the nasal mask and the timer includes an hour meter. Whenthe sensed nasal pressure exceeds a predetermined level indicating thatthe mask is in place about the patient's nose, the hour meter isactivated to register accumulated usage time.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of the preferred respiratoryapparatus;

FIG. 2 is an electrical schematic diagram of the compliance circuit ofFIG. 1; and

FIG. 3 is an electrical schematic of a second embodiment of thepreferred compliance circuit.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring initially to FIG. 1, preferred respiratory apparatus 10includes gas delivery unit 12, and compliance circuit 14. Gas deliveryunit 12 includes pressure supply device 16 and patient connector 18.Pressure supply device is preferably a conventional respiratory therapydevice operable for delivering ambient air at a selected pressure suchas the COMPANION 318 nasal CPAP system available from Puritan-Bennett ofLenexa, Kans. The preferred patient connector 18 is known as an ADAMcircuit also available from Puritan-Bennett and further includesconnection hose 20 and nasal mask 22.

FIG. 2 illustrates compliance circuit 14, which includes adjustablepressure switch 24 (P/N MPL-500-P-G-40 available from Micro PneumaticLogic Co.), hose 26 pneumatically interconnecting mask 22 and switch 24,and timer circuit 28. Circuit 28 includes capacitor C1 (0.1 uF), voltageregulator 30 (type 7508), capacitor C2 (0.1 uF), capacitor C3 (10.0 uF),resistor R1 (500 Ohms), light emitting diode (LED), and time meter 32(P/N T33BM733-DC from ENM Co.).

In use, pressure switch 24 is adjusted to close at a pressure level justbelow that of the CPAP pressure prescribed for the patient. When device16 is turned on and mask 22 properly fitted, pressure at the prescribedlevel is delivered to the patient and also delivered by way of hose 26to switch 24, which closes. In this way, hose 26 and switch 24 presentan effective means for sensing the pressure at nasal mask 22, which is aparameter indicative of the status of usage of unit 12 by the patient.More particularly, pressure above the pressure switch setting indicatesthat the patient is using apparatus 10, and pressure below this settingindicates the status of non-usage.

With switch 24 closed, power at 12 VDC (supplied by device 16) isdelivered to capacitor C1 and to the input of voltage regulator 30,which supplies a regulated output at +5 VDC to capacitors C2, C3,resistor R1, and meter 32. With this supply voltage, meter 32 isactivated as is the LED by way of resistor R1. While activated, meter 32records accumulated time.

If mask 22 becomes dislodged or not properly seated thereby presentingexcessive leakage, the pressure inside mask 22 drops substantially belowthe set point pressure. When this occurs, switch 24 opens to de-energizetimer circuit 28 and deactivate meter 32.

FIG. 3 illustrates circuit 34 which is a second embodiment of thepreferred compliance circuit. The input to this circuit is provided atterminal 36 and is preferably in form of logic signals such as a voltageat +9 VDC during exhalation of a patient and at 1.0 VDC during patientinhalation. Such an input can be provided, for example, by aconventional flow transducer placed in connection hose 20 withappropriate interface circuitry to provide the desired logic signalscorresponding to patient exhalation and inhalation. With such anarrangement, air flow through hose 20 provides an indication of whetherthe patient is respirating, at least in part, through hose 20. Thedesired input signals could also be provided through other meansresponsive to patient respiration such as a pressure transducer in mask22, a current monitor coupled with the blower motor of device 16, a heatsensor in the mask, or a position sensor coupled with a control valvethat might be used to control the pressure delivered to the patient.

Circuit 34 includes network 38 composed of resistors R2 (1 K), R3 (1 M),diode D2 (type 4148) and capacitor C4, inverter network 40, inverternetwork 42, field effect transistor T1 and meter 32. Networks 40 and 42include operational amplifiers A1 and A2 respectively interconnectedwith various resistors as shown in FIG. 3 so that these respectivenetworks function as simple inverters.

In the operation of circuit 34, a logic high input at +9 VDC at terminal36 corresponds to patient exhalation. This input rapidly chargescapacitor C4 through resistor R2 and diode D2. Amplifier A1 inverts thissignal to a logic low input to amplifier A2 which again inverts toprovide a logic high output to the gate of transistor T1, which turns onand thereby activates meter 32.

When the input at terminal 36 goes low (+1 VDC) during patientinhalation, capacitor C4 discharges slowly through resistor R3. Moreparticularly, the time constant of resistor R3 and capacitor C4 is about10 seconds which maintains the logic high input to amplifier A1 duringnormal patient inhalation (lasting less than 10 seconds). The nextpatient exhalation results in recharging of capacitor C4. In this way,the operation of meter 32 is maintained during the entire respiratorycycle of the patient and thereby accurately accumulates the usage timeof apparatus 10 by the patient.

If the patient removes mask 22, or excessive leaks develop, a subsequentexhalation signal is not provided at terminal 36 to recharge capacitorC4. After 10 seconds, the input voltage to amplifier A1 is sufficientlylow so that a logic high output is provided to amplifier A2 which inturn provides a logic low output to the gate of transistor T1 whichturns off and de-energizes meter 32.

As those skilled in the art will appreciate, the present inventionencompasses many variations in the preferred embodiments describedherein. For example, the invention finds utility in the context of CPAP,IPAP, and other pressure regimens. Additionally, a wide variety ofinputs can be provided indicative of patient usage of the therapeuticapparatus so that the actual time of usage can be determined.

Having thus described the preferred embodiments of the presentinvention, the following is claimed as new and desired to be secured byLetters Patent:
 1. A respiratory apparatus comprising:a gas deliveryunit including coupling means for coupling with a patient's airway anddelivery means for delivering a breathable gas thereto during usage ofsaid unit by a patient; and a compliance circuit responsive to said gasdelivery unit and that senses a parameter indicative of the status ofusage of said unit by a patient, said compliance circuit including anadjustable pressure switch, timer means for determining accumulated timeof usage of said unit by a patient and logic means generating logicsignals responsive to patient breathing cycles and for communicatingwith said adjustable pressure switch to activate and deactivate saidtimer means.
 2. The apparatus as set forth in claim 1, said deliveryunit including means for delivering said breathable gas under pressurefor at least a portion of a patient's respiratory cycle wherein saidpressure is sufficient for the treatment of obstructive sleep apnea. 3.The apparatus as set forth in claim 1, said breathable gas includingambient air.
 4. The apparatus as set forth in claim 1, said couplingmeans including means for coupling with a patient's nasal passages. 5.The apparatus as set forth in claim 1, said delivery unit includingmeans for delivering said breathable gas under a selected pressure forat least a portion of a patient's respiratory cycle.
 6. The apparatus asset forth in claim 5, said compliance circuit including means fordetecting a drop in said selected pressure below a predetermined level,such being indicative of uncoupling of said delivery unit from apatient's airway and thereby indicative of a lack of usage of said unitby a patient.
 7. The apparatus as set forth in claim 6, said timer meansincluding a selectively activatable, accumulated time meter and meansfor activating said meter in the absence of said drop in said selectedpressure below a predetermined level.
 8. The apparatus as set forth inclaim 1, said compliance circuit including means for detecting the flowof said gas to a patient and for detecting the occurrence of said flowabove a predetermined level, such being indicative of uncoupling of saiddelivery unit from a patient's airway and thereby indicative of a lackof usage of said unit by a patient.
 9. The apparatus as set forth inclaim 8, said timer means including a selectively activatable,accumulated time meter and means for activating said meter in theabsence of said occurrence.
 10. The apparatus as set forth in claim 1,said timer means including a selectively activatable, accumulated timemeter and means for activating said meter during usage of said unit by apatient.
 11. A respirator apparatus comprising:a breathing gas supply; apatient connector in fluid communication with said breathing gas supply;a meter configured to accumulate time of usage of said breathing gassupply by a patient; and logic means for generating a signal indicativeof usage of said breathing gas supply by a patient, said logic meansincluding first means for generating a logic signal corresponding topatient exhalation and second means responsive to said logic signal forenergizing and de-energizing said meter.
 12. A respiratory apparatus asrecited in claim 11, wherein said first means also generates logicsignals corresponding to patient inhalation.
 13. A respiratory apparatusas recited in claim 11, wherein said patient connector includes meansfor coupling with a patient's nasal passages.
 14. A respiratoryapparatus comprising:an ambient air blower; a pneumatic hose in fluidcommunication with said blower; a nasal mask in fluid communication withsaid pneumatic hose and said blower; a pressure sensor for generating asignal indicative of connection of said nasal mask to a patient; a timeractivated by said pressure sensor, said timer being configured toaccumulate an amount of time said nasal mask is connected to a patient;and logic means for generating logic signals responsive to patientbreathing cycles and for communicating with said pressure sensor toactivate and deactivate said timer.
 15. A respiratory apparatus asrecited in claim 14, wherein said pressure sensor includes a switchwhich activates said timer when a prescribed pressure is maintained atsaid nasal mask and which deactivates said timer when a prescribedpressure is not maintained at said nasal mask.
 16. A respiratoryapparatus comprising:supply means for delivering breathable gas under aselected pressure for at least a portion of a respiratory cycle of apatient; a patient connector in fluid communication with said supplymeans, said patient connector including means for coupling with apatient's nasal passage; timer means including a selectivelyactivatable, accumulated time meter; logic means for generating a signalindicative of said patient connector being coupled to a patient's nasalpassage, said signal responsive to patient breathing cycles; and meansfor activating and deactivating said timer means in response to thesignal from said logic means.
 17. A respiratory apparatus as recited inclaim 16, wherein said logic means includes means for detecting areduction in the selected pressure below a predetermined level, suchbeing indicative of uncoupling of said patient connector from apatient's nasal passage and thereby indicative of a lack of usage of therespiratory apparatus by a patient.
 18. A method for measuring thecompliance of a patient using a respiratory apparatus, the methodcomprising:providing a breathing gas supply and a patient connector influid communication with the breathing gas supply; generating a firstand a second logic signal, said first logic signal corresponding topatient exhalation indicative of usage of the breathing gas supply by apatient; and said second logic signal corresponding to nonusage of saidgas supply by a patient; activating a meter in response to said firstlogic signal to accumulate time of usage of the breathing gas supply bya patient; and deactivating said meter in response to said second logicsignal.
 19. A method for measuring the compliance of a patient using arespiratory apparatus as recited in claim 18, wherein said generating alogic signal step includes generating a logic signal corresponding topatient respiration through the patient connector.
 20. A method formeasuring the compliance of a patient using respiratory apparatus, themethod comprising:delivering breathing gas under a selected pressure forat least a portion of a respiratory cycle of a patient; providing apatient connector in fluid communication with the breathing gas, apatient connector including means for coupling with a patient's nasalpassage; generating a logic signal indicative of the patient connectorbeing coupled to a patient's nasal passages, said signal responsive topatient breathing cycles; and activating and deactivating an accumulatedtime meter in response to the logic signal.
 21. A method for measuringthe compliance of a patient using respiratory apparatus as recited inclaim 20, wherein said generating a logic signal step includes detectinga reduction in the selected pressure below a predetermined level, suchbeing indicative of uncoupling of the patient connector from a patient'snasal passage and thereby indicative of a lack of usage of therespiratory apparatus by a patient.
 22. A method for measuring thecompliance of a patient using respiratory apparatus as recited in claim20, wherein said generating a logic signal step includes detecting aflow of the breathing gas and detecting the occurrence of the flow ofthe breathing gas above a predetermined level, such being indicative ofuncoupling of the patient connector from a patient's nasal passage andthereby indicative of a lack of usage of the respiratory apparatus by apatient.
 23. A respiratory apparatus comprising:a gas delivery unit forproviding gas flow, said gas delivery unit including a blower motorhaving a measurable current; a patient connector in fluid communicationwith said gas delivery unit, said patient connector configured toprovide gas flow to a patient; a compliance circuit including a meter,said compliance circuit responsive to at least one input signal, saidmeter configured to accumulate time of usage of said gas delivery unit;and a current monitor coupled with said blower motor, said at least oneinput signal varying with the current of said blower motor, wherein thecurrent provides an indication of patient respiration through saidpatient connector.
 24. A respiratory apparatus comprising:a gas deliveryunit for providing gas flow; a patient connector in fluid communicationwith said gas delivery unit, said patient connector configured toprovide gas flow to a patient; a compliance circuit including a meter,said compliance circuit responsive to at least one input signal, saidmeter configured to accumulate time of usage of said gas delivery unit;and a heat sensor located proximate said patient connector, said atleast one input signal varying with a temperature change of gas flowthrough said patient connector, wherein said heat sensor provides anindication of patient respiration through said patient connector.
 25. Arespiratory apparatus comprising:a gas delivery unit for providing gasflow, said gas delivery unit including a control valve having a positionfor regulating gas flow; a patient connector in fluid communication withsaid gas delivery unit, said patient connector configured to provide gasflow to a patient; a compliance circuit including a meter, saidcompliance circuit responsive to at least one input signal, said meterconfigured to accumulate time of usage of said gas delivery unit; and aposition sensor coupled to said control valve, said at least one inputsignal varying with the position of said control valve, wherein saidposition sensor provides an indication of patient respiration throughsaid patient connector.
 26. A respiratory apparatus comprising:a gasdelivery unit including coupling means for coupling with a patient'sairway and delivery means for delivering a breathable gas thereto duringusage of said unit by a patient; and a compliance circuit responsive tosaid gas delivery unit and that senses a parameter indicative of statusof usage of said unit by a patient, said compliance circuit includingtimer means for determining accumulated time of usage of said unit by apatient and logic means for generating at least one logic signalcorresponding to a patient's breathing cycle, said logic means furtherincludes means for maintaining operation of said timer means during apatient's breathing cycle.